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Forum Index : Microcontroller and PC projects : GPS speed and distance calculations
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Keith @ Senior Member  Joined: 19/06/2011 Location: AustraliaPosts: 167 |
Hi Ben You are using a SiRF3 receiver which is very high spec.... http://gpstekreviews.com/2007/04/14/gps-receiver-chip-perfor mance-survey/ Sub second polling info ... http://gpsd.berlios.de/hacking.html#subsecond Looks like SiRF and NMEA may not be the way to go for sub second polling .. that should narrow the field down a little! Also looks like the US will be augmenting the GPS bands for us civilians some time in the future ... http://en.wikipedia.org/wiki/Global_Positioning_System Keith The more we know, the more we know we don't know ! |
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| Keith @ Senior Member Joined: 19/06/2011 Location: AustraliaPosts: 167 |
Hi Ben was wondering how you are going with your project? for a little entertainment have look at this HUD navigation system ... http://www.physorg.com/news/2011-10-head-up-prize-munich.htm l Keith The more we know, the more we know we don't know ! |
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| Olimex Senior Member Joined: 02/10/2011 Location: BulgariaPosts: 226 |
you can look at this project http://lea.hamradio.si/~s53mv/navsats/theory.html it's done many years ago but the GPS theory hasn't changed since then |
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trippyben Regular Member  Joined: 26/06/2011 Location: AustraliaPosts: 91 |
No significant progress recently Keith, there's already a couple of GPS pulse senders on the market - see hummingbird electronics in Australia (not the fish finder mob) Whilst they advertise 5Hz update, i doubt that the actual navigation update is any faster than 1Hz. They may be interpolating in order to improve tight corner accuracy - I don't know for sure. These units offer good on-road accuracy according to one of my customers who uses them - same as i have found. I've still got it ticking over in the car, been playing with the OLED display instead of the GPS! I am liking the 32bit pic and will soon put together a list of features for my next tripmeter prototype. I think it will include the GPS module as an option to help with calibration and to be a backup if a wheel sensor fails. Olimex, your link didn't work??? |
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| Keith @ Senior Member Joined: 19/06/2011 Location: AustraliaPosts: 167 |
Ben try this translated link http://translate.google.com.au/translate?hl=en&sl=sl&tl=en&u =http%3A%2F%2Flea.hamradio.si%2F then look down the list to "S53MV ....." and click on that and look for "my experimental & low weight avionics" on the next page and click on that I think this is the subject. Keith The more we know, the more we know we don't know ! |
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| Olimex Senior Member Joined: 02/10/2011 Location: BulgariaPosts: 226 |
i forgot that to post url here is done in special way here is the link again it's in english so no need for google translation http://lea.hamradio.si/~s53mv/navsats/theory.html |
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| Keith @ Senior Member Joined: 19/06/2011 Location: AustraliaPosts: 167 |
Thanks Olimex I've had a quick look and as per usual I'll stick with the operator manual and leave the Newtonian maths to the real geeks ... I've looked at some of this type of info previously. I note that the update rate mentioned in the text is >860ms. I understand the military systems are much faster. I have seen a figure of 20hz supposedly available to the US military in one article. I need some java (coffee). Keith The more we know, the more we know we don't know ! |
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| Keith @ Senior Member Joined: 19/06/2011 Location: AustraliaPosts: 167 |
Ben Good news ... I've come across a 10hz update GPS receiver!!!! I haven't checked it out yet or the prices elsewhere. http://www.oceancontrols.com.au/GPS-002.html regards keith The more we know, the more we know we don't know ! |
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| Vikingboy Regular Member Joined: 23/09/2011 Location: AustraliaPosts: 82 |
Hi Keith, Although I don't know a great deal about GPS etc, A little while ago I was investigating GPS units to experiment with and found this one at 4d Systems: http://www.4dsystems.com.au/prod.php?id=106 When I read your post here I went back and checked, this unit also has 10Hz refresh according to the spec sheet, it looks like quite a nice unit to me and I was considering getting one to play with on the Maximite. rgds, Andrew PS Its also only $29 and comes complete with aerial. |
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| Keith @ Senior Member Joined: 19/06/2011 Location: AustraliaPosts: 167 |
thanks Andrew There's some really good info associated with the module I'm still to determine exactly how they manage to get up to 10hz. I'm curious why they set the default to 1 second if it can achieve a max of .1 second then why not default to .5 second even if it can be set by the user. Given the limited time available in 1 second to handle the calculations, transmission of data and display will it really fit in 10 cycles in all applications. Keith The more we know, the more we know we don't know ! |
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| trippyben Regular Member Joined: 26/06/2011 Location: AustraliaPosts: 91 |
Herein lies the problem with the "10Hz" modules. The data on the Ocean controls module is pretty useless. No info that I could see on how to turn it up to 10Hz? the 4D one is better, but I stll can't find the info on how to increase the output above 1Hz? (i could have missed it???) Maybe you have to use Binary mode and just poll it faster. No mention in either datasheet on the navigational update rate. Others that I have seen specify the data rate and navigation update rate separately. All faster than 1Hz units i've seen so far still only have a 1Hz navigation update, and therefore I can't see how the faster data rate is of any advantage. Ben |
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| Buchan Newbie  Joined: 25/09/2011 Location: AustraliaPosts: 12 |
G'Day Folks, I'm running the Ocean Controls GPS-002 to either my PC or MaxiMite, as the job requires. How do you get a stable position (lat/lon) when stationary. Is it because I am only looking for the GPRRC message and not the checking that it is the same SAT number I took the first reference point from or something else.? Regards, Doug. Even farmers need computers |
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| Keith @ Senior Member Joined: 19/06/2011 Location: AustraliaPosts: 167 |
Hey Doug You need to give a bit more info ... how have you got GPS module connected eg SPI. What software are you running on the Maximite? Can you provide a copy or at least some details. Also do you have a minimum of 3 satellites in the $GPGSA sentence this will give minimum accuracy. Also is the speed zero in the GPS data. I am assuming that you have the same problem whether it is connected to the PC or to the Maximite since you mention both devices in the same sentence. Keith The more we know, the more we know we don't know ! |
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| Buchan Newbie Joined: 25/09/2011 Location: AustraliaPosts: 12 |
G'Day Keith, GPS-002 is connected as COM2. MM Ver 2.6. Problem is same on PC using GPS Locator and Visual GPS. On the PC programs, we see several sat's at good signal strength. (there is no difference in antenna location in these tests) When stationary, both PC programs show continually changing last 3 digits in lat & lon. This is also the case on MMite MM Program is similar to GPS.BAS from Geoff's library, which only looks for 'GPRMC' string to load data. (sorry, spelling mistake in first post) GPS part of code shown below. Still contains parts to display on screen as well as LCD, as this code still under test before being imbedded with other hardware and program parts using a mini-MM.. Regards, Doug. 500 ' Outputting GPS data 510 DO ' loop forever 520 GOSUB 800 ' get the next line 530 IF arg$(0) = "GPRMC" THEN ' GPRMC contains lat/long 540 IF arg$(2) = "A" THEN ' "A" means locked on to satellites 550 PRINT "Latitude = "; LEFT$(arg$(3), 2); " "; MID$(arg$(3), 3); 560 PRINT " "; arg$(4); 570 PRINT " Longitude = "; LEFT$(arg$(5), 3); " "; MID$(arg$(5), 4); 580 PRINT " "; arg$(6) 581 z$="LAT":a$=LEFT$(arg$(3),2):b$=MID$(arg$(3),3):c$=arg$(4):d $=" " 582 LCD_line1$=z$+ a$+ d$+ b$+d$+c$ 583 y$="LON":e$=LEFT$(arg$(5),3):f$=MID$(arg$(5),4):g$=arg$(6) 584 LCD_line2$=y$+e$+d$+f$+g$ 586 GOSUB 12000 590 ELSE 600 PRINT "GPS searching..." 602 LCD_line1$= "GPS searching..." : LCD_line2$="for satelites..." 604 GOSUB 12000 610 ENDIF 620 ENDIF 630 LOOP |
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| Keith @ Senior Member Joined: 19/06/2011 Location: AustraliaPosts: 167 |
Doug I have checked a couple of Garmin units using decimal degrees ie hddd.ddddd and I observed a bit of variation in the last digit not much given I only had 4 satellites in view but speed was zero. Your GPS module seems to be the common denominator as it's the same on the PC & MM. Using GPRMC data can you check your speed over ground (field 7) to see if it is zero when it is not moving ie 000.0 and do this over about 5 to 10 minutes. If the GPS speed on your unit is zero I would collect some raw LAT/LON data from GPRMC and see what the variation is over a certain period of time to see if it is cyclical or random and to quantify the amount of variation. Plug it into a spreadsheet and sort it and graph it etc. Or wait to see what other replies you get! Keith The more we know, the more we know we don't know ! |
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| Talbit Senior Member Joined: 07/06/2011 Location: AustraliaPosts: 210 |
Doug, I've almost finished my GPS clock using a Trimble Ace 3 module. Do you want the code? I don't want to study the whole post - I guess I should - I might learn something! I can get it to display the clock or the position but not both at this stage. I'm about to impliment the push button (interrupt) to get it to do that. My position seems rock solid but I've only tested it in a stationary position. If you feed the NMEA string from the GPS into Tera Term you should see the positions in the GPRMC sentences and if you are stationary, they shouldn't change. I recon it's your GPS jittering around. I'm not familiar with yours. Is there a setting that's wrong? Talbit. Talbit |
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| Talbit Senior Member Joined: 07/06/2011 Location: AustraliaPosts: 210 |
Doug, I've just noticed... Your code... 581 z$="LAT":a$=LEFT$(arg$(3),2):b$=MID$(arg$(3),3):c$=arg$(4):d $=" " You've got a space between the d and $ Would that cause your problem? It shouldn't but it might make a mess of you LCD display. Talbit Talbit |
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TassyJim Guru  Joined: 07/08/2011 Location: AustraliaPosts: 6098 |
Most GPS units will wander about a bit when stationary. Even the AIS unit on my local lighthouse moves about. (Tassy is not that unstable) On some units you can change a setting to cause the GPS to appear stationary if the movement is not more than a few metres Jim VK7JH MMedit MMBasic Help |
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| Buchan Newbie Joined: 25/09/2011 Location: AustraliaPosts: 12 |
G'Day Folks, Thank's for your replies. I just looked at my code file, line 581 is correct in the file, don't know where the space came from. The code was just a Q&D way of getting it to function to complete a job on time. I'm about to reconnect the GPS-002 engine to my PC later and do a static study using Visual GPS. I can store the data and check what is happening. Also will check the data sheets etc. and see what I can get from that. I forgot to say, GPS-002 is connected as COM2 @ 9600. Would like to see the relevant bit of code Talbit, if that's ok. Regards, Doug. |
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| Talbit Senior Member Joined: 07/06/2011 Location: AustraliaPosts: 210 |
Doug, Just finalising some more bits. I should have it in a more presentable form soon. But for now, look at my GPS Clock 26 September 2011. It's a bit different now but basically the same as far as the reading of the NMEA strings. I did have a closer look at my strings coming directly from the Trimble. The last few digits do change a bit but only over time. They certainly don't jitter around Regards Talbit Talbit |
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